1. Field of the invention:
This invention relates to a semiconductor laser array device with stabilized operation characteristics.
2. Description of the prior art:
With the advance of semiconductor laser devices that produce high output power, more attention has been paid to semiconductor laser array devices. For the production of semiconductor laser array devices, there are mainly three crystal growth methods, molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), and liquid phase epitaxy (LPE). A semiconductor laser array device that is produced by LPE has been proposed by Matsumoto; Journal of Applied Physics, vol. 58(7), P 2783-2785 (1985) in which a V-channeled substrate inner stripe (VSIS) structure with three waveguides is disclosed. FIGS. 16A to 16C show the production process of a semiconductor laser array device with ten waveguides. On a p-GaAs substrate 301 an n-Al.sub.0.1 Ga.sub.0.9 As current blocking layer 302 with a thickness of 0.7 .mu.m and an n-GaAs protective film 303 with a thickness of 0.1 .mu.m are successively formed by LPE (FIG. 16A). Then, ten grooves 320 with a width of 4 .mu.m each, a depth of 0.9 .mu.m each and a pitch of 5 .mu.m are formed by a photolithographic technique and an etching technique in such a way that they reach the substrate 301 through both the current blocking layer 302 and the protective layer 303 (FIG. 16B). Then, on the protective layer 303 including the grooves 320, a p-Al.sub.0.4 Ga.sub.0.6 As cladding layer 304 having a thickness of 0.3 .mu.m in the areas over the protective layer 303, an Al.sub.0.1 Ga.sub.0.9 As active layer 305 with a thickness of 0.8 .mu.m, an n-Al.sub.0.4 Ga.sub.0.6 As cladding layer 306 with a thickness of 1.2 .mu.m, and an n-GaAs contact layer 307 having a thickness of 1.5 .mu.m are successively formed by LPE (FIG. 16C). The semiconductor laser array device produced in this way is disadvantageous in that the grooves 320 are not completely filled with the p-cladding layer 304, resulting in a bend of the active layer 305, which causes a weakness of the optical-coupling between the adjacent waveguides. Thus, laser oscillation occurs in the individual waveguide, which causes difficulties in attaining laser oscillation in a synchronous phase mode.